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What is a HIT blood test?

What is a HIT blood test?

A test for heparin-induced thrombocytopenia (HIT) antibody, also called heparin-PF4 antibody, is performed to detect antibodies that develop in some people who have been treated with heparin.

What is a positive HIT antibody?

The test is considered positive if the sample causes a greater than 20% serotonin release at a (therapeutic) dosage of 0.1 U/mL heparin. The14C-SRA is considered the “gold standard” assay for the detection of heparin-dependent antibodies in heparin-induced thrombocytopenia (HIT).

What is a positive HIT?

Abstract. Heparin‐induced thrombocytopenia (HIT) is a potentially devastating immune mediated adverse drug reaction caused by the emergence of antibodies that activate platelets in the presence of heparin.

What is the role of PF4?

Its major physiologic role appears to be neutralization of heparin-like molecules on the endothelial surface of blood vessels, thereby inhibiting local antithrombin activity and promoting coagulation. As a strong chemoattractant for neutrophils and fibroblasts, PF4 probably has a role in inflammation and wound repair.

How do you confirm hits?

Diagnosis of HIT is based on clinical assessment and laboratory results. Primary laboratory tests for HIT include immunologic assays, such as an enzyme-linked immunosorbent assay (ELISA), and functional, platelet-activation assays, such as the serotonin release assay (SRA).


Type 2 HIT is an immune-mediated disorder that typically occurs 4-10 days after exposure to heparin and has life- and limb-threatening thrombotic complications. In general medical practice, the term HIT refers to type 2 HIT.

How is HIT diagnosed?

HIT can often be diagnosed by measuring the platelet count and PF4 antibody level in the blood. Symptoms of new blood clot formation may suggest HIT. Symptoms of deep vein thrombosis include pain or tenderness, sudden swelling, discoloration, visibly large veins, and skin that is warm to the touch.

Can a negative H / PF4 antibody exclude the diagnosis of hit?

Because up to 10% of patients with clinical heparin-induced thrombocytopenia (HIT) may have a negative H/PF4 antibody ELISA result, a negative H/PF4 antibody ELISA result does not exclude the diagnosis of HIT when clinical suspicion remains high.

What are the criteria for SRA negative hit?

We defined SRA-negative HIT as patients meeting three criteria: clinical picture compatible with HIT (4Ts ≥ 4 points); EIA-positive (≥1.00 units); and PF4-SRA-positive. Among 430 patients, 35 were EIA-positive/SRA-positive and 27 were EIA-positive/SRA-negative.

What do you need to know about hit?

Guide clinical decision-making in patients with a current or previous diagnosis of HIT HIT is a clinicopathologic diagnosis that requires combined evaluation of clinical examination and laboratory test results.

Are there false positives on the HIT antibody test?

The interpretation of HIT antibody results relies upon testing only people who have a moderate to high probability of having HIT II. Both false negatives and false positives can occur with this test and are more likely in those with a low probability of having HIT II.